This invention relates to a method of writing data on a length of multitrack magnetic tape in tape transports used as peripheral devices of computer systems, and to such a tape itself on which data is written in accordance with the invention. The writing method of this invention has particular utility with two-reel, belt driven, multitrack tape cartridges of the type disclosed in U.S. Pat. No. 3,692,255 filed by Behren and assigned to Minnesota Mining and Manufacturing Company, of Minn., the United States, although it is not desired that the invention be limited to this particular type of tape.
The two-reel tape cartridge according to Behren employs a flexible belt for driving the tape between a pair of reel hubs. The belt extends along a belt guide path around guide rollers adjacent the reel hubs and a driving roller therebetween and contacts the tape on the reel hubs. The rotation of the driving roller causes the belt to frictionally drive the tape reels to tension the tape and to move the tape between the reels. The cartridge construction offers the advantages of low power bidirectional drive and rapid acceleration and deceleration of the tape by a single reversible drive motor.
A problem with the above and other comparable tape cartridges is that, as has proved by measurement, the tension of the tape at its portion adjacent the transducer rises linearly as it travels from the beginning toward the end, and back from the end toward the beginning, of the tape. Reasons for such linear variations in tape tension are not necessarily clear, but it seems most reasonable to ascribe them to varying tape diameters on the reel hubs.
Thus, regardless of whether the tape is driven forwardly or reversely, the tape tension is too low for error-free writing or reading immediately after it has started traveling from its beginning or end. A conventional solution to this problem was to start writing on each of the tracks in a longitudinal tape position where the tape tension had built up sufficiently high. This solution is unsatisfactory because not the full tape length is utilized for data storage.